1. Field of the Invention
This invention relates to a monoester compound of a 2,2'-alkylidene bis(4,6-di-substituted phenol and to a method of preparing such a monoester compound.
2. Description of the Prior Art
In order to prevent articles of synthetic resins from reducing their commercial value due to deterioration and discoloration by heat and light or oxides of nitrogen fumes, various stabilizers for synthetic resins including antioxidants and their improvements have been proposed. For this purpose, light stabilizers, sulfur type antioxidants, phosphites and phenol type antioxidants have been used either alone or in combination. Many of these stabilizers, however, are still not sufficient in their stabilizing effect over a long period of time since they are unstable as such to heat or air oxidation and further, some of them discolor synthetic resins by the action of atmospheric oxides of nitrogen. In general, antioxidants against deterioration by the action of light having a much improved stabilizing effect tend to discolor synthetic resins by the action of heat and light or oxides of nitrogen fumes. On the other hand, antioxidants having a high resistance to oxides of nitrogen fumes are inferior in their stability against deterioration by the action of light. Thus, these stabilizers do not have the antideterioration effect and anit-discoloration effect simultaneously at a satisfactory level. For example, U.S. Pat. No. 3,642,669 describes alkoxy substituted, sterically hindered phenols having a 2-(2'-hydroxy-3'-tertiary alkyl benzyl)-anisole unit as the stabilizer for polyurethanes against light and hot air. Their anti-discoloration effect against atmospheric oxides of nitrogen fumes and anti-deterioration against light are still not sufficiently satisfactory. U.S. Pat. No. 3,428,711 describes the use of a copolymer of diisopropylaminoethyl methacrylate and decyl methacrylate as an anti-discoloring agent against atmospheric oxides of nitrogen and 4,4'-butylidene bis(6-tert-butyl-m-cresol) as an anti-oxidant in combination for the stabilization of polyurethanes against ultraviolet radiation and fume. Further, Japanese patent application (OPI) 29352/1978 describes the use of a hydrazinotriazine derivative and a sulfur-containing acid ester compound in combination for the stabilization of polyurethanes against discoloration. Such a combination, however, has not a sufficient effect on anti-discoloration and retention of the desirable properties of the original polyurethane such as strength. Japanese patent application (OPI) 29850/1977 describes a polyester including, as it representative, [2-(2"-hydroxy-3'-tert-butyl-5'-methylbenzyl)-4-methyl-6-tert-butylphenyl] terephthalate as the stabilizer of polyurethane. This stabilizer has an anti-discoloration effect but its effect is not enough. Moreover, the stabilizer disadvantageously bleeds from the surface of polyurethane articles. As widely employed antioxidants, there can be mentioned 2,2'-isobutylidene bis(4,6-dimethyl-phenol), 2,2'-methylene bis(4-methyl-6-tert-butylphenol), 2,2'-(3,5,5-trimethylhexylidene)-bis(4,6-dimethylphenol) and 2,2'-methylene bis(4,6-dimethylphenol) but they are disadvantageously discolored as such. Yet stabilizers which have better anti-deterioration effect and anti-discoloration effect on synthetic resins at the same time have been sought.